At the union of the gatehouse with the northern curtain, in the latter, at the level of the water’s edge, is a low-browed archway, which could only have been accessible by a boat, and is a water gate. It is defended by two grates, and a cavity open above between them, and thence a covered way, once probably a sort of canal, leads close under, and north of, the dividing wall, to the edge of the inner moat.
This curtain runs northward for 130 yards, and is strengthened exteriorly by three buttress towers, quadrangular and solid below, but hexagonal and chambered above. Each has a projection of 20 feet; they are of unequal breadth. The chambers have each a loop in front, and one at the junction of the tower with the wall on either side. They were accessible only from the rampart.
In the curtain itself are six loops, opening in pairs between the buttress towers. The curtain ends, northward, in a pair of towers, connected by the vault of a portal, the north postern, regularly defended, and opening upon a plot of ground and causeway separating the two parts of the outer moat.
Behind, and parallel to this curtain, at a distance of 19 feet, was a slight wall, 4 feet thick, which formed the back wall of a postern gallery, leading from the gatehouse to the north postern, and forming above a broad flat walk for the defence of the ramparts. This gallery is said to have been fitted up as a stable.
Southern Curtain.—The general plan of this curtain is irregular; it passes south-eastward from the gatehouse, forms a large semicircle, and, passing off in a long straight wall, crosses the Nant-y-Gledyr, and terminates in a tête-du-pont and a postern. This wall contains a large mural garderobe tower at its angle, and is supported exteriorly by seven quadrangular solid buttresses. In one place it is perforated for the discharge of the waste waters of the mill, and in another for the passage of the Nant-y-Gledyr, being, at that part, where subjected to great pressure, 15 feet thick. This curtain is accessible from the tête-du-pont; and upon it, through the garderobe tower is a mural chamber, serving as a “place d’armes.” The face of the wall, between the buttresses, is wrought into a concavity, increasing towards the summit, so that any missile dropped from it would be projected outwards. The soil of the platform behind this curtain is 25 feet above the exterior level.
The Platform is a large surface of sward behind the southern curtain, between it and the counterscarp of the inner moat; upon it stood the mill, and from it dropped the inner drawbridge. It increases in breadth from the dam to the dividing wall, where it measures 94 feet.
The Tête-du-pont terminates the southern curtain. It consists of a curve of the wall, westward, into a semicircle, with towers and a postern gate, protected by a bifurcated wall, intended to prevent the curtain from being outflanked. It rests upon the outer edge of the lake.
In front of this great line of defence is a moat, about 60 feet wide, and crossed by a double drawbridge of two spans of 18 feet each at the great gateway, connected with a large pier in the centre of the moat, capable of being converted into a sort of barbican. This moat communicates with, and admitted of being filled from, the Nant-y-Gledyr.
Such is the principal front and eastern line of defence, not only calculated to withstand attacks from the front, flanks, or rear, but also capable of being held out, the southern against the northern part.
From the northern extremity of this front, at the northern postern, a bank of earth, lined inwards, or on its southern face, by a wall, and at one part thickened into a dam, divides the middle from the outer moat, at present skirted by the Nant-Garw road. This is the north bank.